The present invention relates to dental restorations, and more particularly to reinforced direct and indirect restorations.
Direct filling materials are materials that are filled into a tooth cavity and then hardened. Currently available dental direct-filling materials include amalgam, composite resin, glass ionomer cement, and resin-glass ionomer hybrid materials. Indirect filling materials are materials that are hardened or fabricated in a dental laboratory and then fitted either into a tooth cavity or onto a prepared tooth in a dental clinic.
Dental amalgam has been widely used as a direct-filling material for more than a century. The mercury that amalgam contains, however, raises concerns about its toxicity and environmental hazards. As a result, an increasing number of countries have discontinued or are discontinuing the use of amalgam (Hickel, 1996, Acad Dent. Mater. Trans. 9:105-129).
Glass ionomer materials, based on acid-base reactions of polyacid with fluorosilicate glass, possess desirable properties such as fluoride release and adhesion to teeth. However, the inferior mechanical properties, especially their extreme brittleness and low strength, have severely limited their use (Wilson and McLean, 1988, Glass-ionomer Cement, Quintessence Pub). The more recently developed resin-glass ionomer hybrid materials possess improved mechanical properties, but they are still not strong enough for use in posterior restorations with significant occlusal contact (Blackwell and Kase, 1996, Acad. Dent. Mater. Trans. 9:77-88; Hickel, 1996, Acad. Dent. Mater. Trans. 9:105-129).
Composite resins, although one of the most promising aesthetic alternatives to amalgam, have drawbacks such as low durability and fracture, especially in large stress-bearing posterior applications (Corbin and Kohn, 1994, JADA125:381-388; Bayneetal., 1994, JADA125:687-701; Wilder et al., 1996, Acad. Dent. Mater. Trans. 9:151-169). The recently developed composite resins exhibit greatly improved wear characteristics, with low wear rates of the composite and the antagonistic enamel (Suzuki et al., 1996, JADA127:74-80). However, to date, composite resins are used only in relatively small restorations with limited occlusal contact without cusp replacement (Wilder et al., 1996, Acad. Dent. Mater. Trans. 9:151-169). The use of composite resins in larger restorations involving cusp replacement is severely limited by the low toughness of the composites. Indeed, analysis of crack propagation in dental restorations confirmed scanning electron microscope observations that composite resin restorations, although exhibiting low wear rates, are prone to bulk fracture with crack propagation rates higher than those of porcelain (Sakaguchi et al., 1992, Dent. Mater. 8:131-136). Clinical observations coupled with finite element analysis showed that during mastication, the inner side of the restoration can be in maximum tension, leading to fracture initiation (Kelly et al., 1995, J Dent. Res. 74:1253-1258).
Reinforcement with continuous fibers has been shown to impart strength, toughness, and fracture resistance to a matrix material (Goldberg U.S. Pat. No. 4,894,012; Scharf U.S. Pat. No. 5,098,304; Goldberg and Burstone, 1992, Dent. Mater. 8:197-202; Adam U.S. Pat. No. 5,445,770). In dentistry, continuous fibers have been proposed for use in the reinforcement of denture base resins (DeBoer et al., J Prosthet. Dent. 51:119-121; Grave et al., 1985, Dent. Mater. 1:185-187; Yazdanie and Mahood, 1985, J Prosthet. Dent. 54:543-547), splints (Levenson, 1986, JADA112:79-80), retainers (Mullarky, 1985, J Clin. Orthod. 19:655-658; Diamond , 1987, J Clin. Orthod. 21:182-183), fixed prosthodonic appliances (Malquarti et al., 1990, J Prosthet. Dent. 63:251-257; Goldberg et al., 1994, J Biomed. Mater. Res. 28:167-173), and more recently fixed partial dentures (Altieri et al., 1994, J Prosthet. Dent. 71:16-22; Freilich et al., 1997, abstract 999, J Dent. Res. 76:138). The use of continuous fibers in tooth cavity restorations, however, has not been pursued. Continuous fibers have not previously been used to fabricate preforms with shapes and sizes suitable for filling into tooth cavities. Continuous fibers have not previously been used for the reinforcement of dental direct-filling restorations. Continuous fibers have not previously been mixed with fluoride-releasing fillers and fabricated into preforms for use in dental restorations.
According to the present invention, a method for direct filling a tooth cavity is provided. A fiber material selected from the group consisting of a hardened fiber composite preform, fibers, an unhardened fiber-resin paste, and a partially-hardened flexible fiber composite preform is inserted into a prepared tooth cavity. Fibers in the fiber material extend continuously across at least 60% of the widest dimension of the tooth cavity. After the fiber material has been placed into the tooth cavity, the rest of the tooth cavity is filled with a conventional direct-filling material. The direct-filling material is then hardened.
According to another aspect of the invention, a method for preparing a dental indirect restoration is provided. A fiber material is placed into a mold having a longitudinal axis. The fiber material is selected from the group consisting of a hardened fiber composite preform, fibers, an unhardened fiber-resin paste, and a partially-hardened flexible fiber composite preform. Fibers in the fiber material extend continuously across at least 60% of the widest dimension of the mold. A composite resin filling material is added to the mold. The filling material is hardened to form the dental indirect restoration.
An indirect dental restoration also is provided by the present invention. The restoration comprises fibers which extend continuously across at least 60% of the widest dimension of the restoration, and a filling resin.
According to yet another aspect of the invention, a method is provided for making a composite fiber preform for direct dental restoration. Fibers are selected from the group consisting of glass fibers, ceramic fibers, polymeric fibers, metal fibers, and mixtures thereof. A resin is coated onto the fibers. The resin is hardened to form a composite fiber preform. Fibers extend continuously through at least 60% of the widest dimension of the preform.
According to a further aspect of the invention, a method is provided for making a composite fiber preform for direct dental restoration. Fibers are selected from the group consisting of glass fibers, ceramic fibers, polymeric fibers, metal fibers, and mixtures thereof. A resin is coated onto the fibers. The resin is hardened to form a composite fiber mass. The composite fiber mass is shaped into a composite fiber preform by at least one of cutting and machining. Fibers extend continuously through at least 60% of the widest dimension of the preform.
A composite fiber preform for dental restorations also is provided by the present invention. The preform includes fibers selected from the group consisting of glass fibers, ceramic fibers, polymer fibers, metal fibers, and mixtures thereof, and a resin. Fibers extend continuously through at least 60% of a widest dimension of the preform.
A dental restoration kit also is provided by the present invention. The kit comprises a preform and a composite filling material. Fibers extend continuously through at least 60% of a widest dimension of the preform.
The present invention thus provides dental restorations, tools and methods for making them, which have improved strength, toughness, and stiffness, and reduced polymerization shrinkage. In addition, the restorations are more easily handled and replaced, and have enhanced aesthetics and wear compatibility.